Dec. 2, 2013
Liquid Metal Interconnects for Conformable Sensor Packaging
Enabling Inertial Measurements of Animals and Soft Robots
Nikolas Kastor and Robert D. White
{[email protected], [email protected]}
iMAPS New England 43rd Symposium & Expo.
Boxborough, MA
Tuesday, May 3, 2016
Sept. 18, 20152
What is a Soft Robot?
• Compliant body.
• Conforms to the environment rather than
manipulating it.
• The idea is:
– Safe around people
– Locomotion in unstructured environments
– Low ordered control
Sept. 18, 20153
Soft Robots
Rus, Daniela, and Michael T. Tolley. "Design, fabrication and control of soft robots." Nature 521.7553 (2015): 467-475.
Sept. 18, 20154
Motivation: Soft Robot Locomotion
• De-coupled Control requires sensing the
position state and configuration.
• Inertial measurement of strategic points.
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Motivation: Biomechanics
– Caterpillar Nociceptive Strike Reflex
• There is an interest in directly measuring the motion of
the caterpillar to determine how it is so fast.• van Griethuijsen, Linnea I., Kelly M. Banks, and Barry A. Trimmer. "Spatial
accuracy of a rapid defense behavior in caterpillars." Journal of
Experimental Biology 216.3 (2013): 379-387.
– Fish Swimming
• Direct inertial measurement of swimming fish is difficult
because of the flexible body and aquatic environment.
• https://sites.tufts.edu/tytelllab/
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Hard Circuits on a Soft Robot
• PCB package technology limits the ‘soft’
functionality of soft-robots.
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Why cant we use Flex Circuits or PCBs?
• Not extensible or compressible (only
bending)
• Not meant for dynamic bending
• Surface mount solder breaks in bending
• Need a package that can deform in 6
degrees of freedom.
elcomdesign.wordpress.com
Sept. 18, 20158
eGaIn Liquid Metal for Interconnects
Eutectic Gallium Indium Alloy
• Properties:
– Liquid @ room temp.
– Melting point at 15.7 °C
– 6.25 g/mL at 25 °C
• Cost: $14.7/gram
• Supplier: Sigma Aldrich
• Hazzard: H314 (corrosive)
μ
1mm
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Prior Art: eGaIn and Conformal Packaging
• eGaIn is used prolifically in the design of soft sensors
and micro-electronics.– Dickey, Michael D., et al. "Eutectic Gallium‐Indium (EGaIn): A Liquid
Metal Alloy for the Formation of Stable Structures in Microchannels at
Room Temperature."Advanced Functional Materials 18.7 (2008): 1097-
1104.
– Tabatabai, Arya, et al. "Liquid-phase gallium–indium alloy electronics
with microcontact printing." Langmuir 29.20 (2013): 6194-6200.
– Tabatabai, Arya, et al. "Liquid-phase gallium–indium alloy electronics
with microcontact printing." Langmuir 29.20 (2013): 6194-6200.
• Packaging of solid state ICs:• Zhang, Bowei, et al. "Flexible packaging of
solid-state integrated circuit chips with
elastomeric microfluidics." Scientific reports 3
(2013).
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Package Design
• 7x7x2 mm PDMS package
• 1x IMU 9250
• 1x 10nF Capacitor 0805
• 2x 0.1μF Capacitor 0805
• 6x 90μm O.D. stranded wire
1mm
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Step 1: Fabricate Micro-Channel Mold
SiSU-8
PE Cavity
• Photo-lithography of SU-8 on silicon.
• 100x50 μm channels
7mm
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Step 2: Place Components
SiSU-8
Component
PE Cavity
• Manually place with forceps under microscope.
7mm
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Step 3: Pin Components in Place
SiSU-8
Component
PE Cavity
Pin
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Step 4: Fill with PDMS
SiSU-8
Component
PE Cavity
Pin
PDMS
• Fill cavity with 25 µL of
PDMS using positive
displacement pipette.
• Cure in place for > 12
hours @ STP.
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Step 5: De-Mold
Component
Pin
PDMS
• Raise pins up and
out of the way.
• A hole remains
where the pin
was placed. This
can be filled later
if desired.
• Extract the
package from the
mold cavity.
Hole
Micro-channels Exposed solder pads
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Step 6: Punch Holes for Filling
Component
PDMS
• Holes are
punched at each
terminal location
for filling eGaIn
and inserting
signal wires.
• Biopsy punches
are too big for this
application, so a
syringe was used
to form the holes.
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Step 7: Apply PDMS Cover Layer
Component
PDMS
PDMS Thin Film
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Step 8: Fill with eGaIn
Component
PDMS
eGaIn
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Step 9: Insert Wires and Seal
Component
PDMS• Wire leads are
inserted for
communication with
the chip.
• The holes are filled
with uncured PDMS.
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Result
Top
Bottom
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Conclusions
• Communication could not be achieved because of
microchannel failure when pressurizing.
• This is possibly due to the air in the channels not diffusing
through the PDMS fast enough.
• 4-wire resistance
measurements of a single trace shows 0 to 300 kΩdrift.
• Something strange is
happening with the eGaIn.
Further characterization of
the material is required.
Sept. 18, 201522
Future Work
• Venting channels
during filling.
• Simplify the process.
• Technique for
attaching to animals Manduca Sexta with IMU on head exhibiting a strike reflex.
Nikolas Kastor, Maxwell Hill, Vishesh Vikas,
Robert D. White and Barry Trimmer, "Semi-
autonomous Soft Robotic Platform for
Terrestrial Locomotion", submitted to the
workshop on "New Frontiers and Applications
for Soft Robotics" at the IEEE/RSJ International
Conference on Intelligent Robots and Systems
(IROS 2015), Hamburg, Germany, October 2,
2015. Submitted August 12, 2015.
• Inertial measurement of soft robot platform.
Sept. 18, 201523
Acknowledgments
• Tufts Soft Material Robotics NSF IGERT-1144591
• Tufts Neuromechanics and Biomimetic Devices Laboratory
http://ase.tufts.edu/biology/labs/trimmer/
• Tufts Micro and Nano Fabrication Facility
http://engineering.tufts.edu/microfab/
• 3D printing was made possible by NSF Award DBI-1126382.
Ritwika
Mukherjee
Anthony
Scibelli
Prof. Barry
Trimmer
Daniela Torres Kevin LigondeDr. Jim Vlahakis
Dr. Vishesh
Vikas
Sept. 18, 201524
Thank you!
Check out our labs!
Microfab:
http://emerald.tufts.edu/~rwhite07/
Soft Material Robotics:
http://ase.tufts.edu/igert/softMaterialRobotics/